Study of the interactions leading to wood resin deposition

In the production of mechanical pulp for paper manufacture, resinous material is released from the wood which can form colloidal dispersions that agglomerate and deposit onto surfaces. These deposits are known as pitch. It is known and cited in literature that the three major components of pitch formed from Pinus radiata extractives are fatty acids (namely those of chain length (C12-C20), resin acids and triglycerides. The major aim of this thesis is to study the interaction between the three major components of wood pitch in order to gain a better understanding of the chemical interactions at a molecular level that cause pitch deposition. The interactions between the main components of the wood extractives; resin acids, fatty acids and triglycerides, have been studied using model compounds in order to investigate the effect of chemical structure on the interactions and deposition tendency. Initially the interaction of just two components interacting with each other was investigated and showed that the difference in chemical structure and properties influenced the interaction and also the propensity to deposit. This difference in the formation of the hydrogen bond and also the stability, or strength, of the hydrogen bond can be used to explain the differences in deposition of fatty acid/resin acid mixtures. Studies undertaken to investigate a three-component system where all three hydrophobic extractives are present resulted in an extension of Qin's model of the structure of a three-component pitch colloid. In this model the hydrophobic extractives, such as triglycerides, form a hydrophobic core and the more hydrophilic extractives, such as resin acids and fatty acids, interact with each other to form a hydrophilic outer layer with their hydrophilic groups extending into the aqueous surroundings. The amount of colloidal pitch deposited was found to be related to the solubility of the hydrophobic core and to the stabilisation energy of the hydrophilic outer layer. The interaction between hemicelluloses and three of the major hydrophobic extractives of Pinus radiata, fatty acids, resin acids and triglycerides was also studied. Hemicelluloses belong to a group of heterogenous polysaccharides and due to their branched hydrophilic nature it is believed that they help to stabilise the colloidal pitch in its aqueous surroundings helping to prevent it from depositing onto surfaces. Through the theoretical calculations of the individual sugar groups and different hemicellulose monomers, predictions were also made concerning the hemicellulose structure that will have the greatest stabilising properties against colloidal pitch.